Anthropogenic stressors contribute to change



  • Historical build-up:
    • hunting and megafaunal extinctions
    • agriculture and domestication
    • urbanization and population growth


  • Current trends (today’s topic)
    • land use change
    • pollution
    • globalization


  • Equivalent to a natural stressor if an organism’s response is similar or identical

Land-use change levels up


  • Before the Anthropocene, human induced land-use change was mostly regional
    • hunting, agriculture and increased urbanization
    • Thus, habitat modification is not new

How have humans modfied 75% of the land surface?


How have humans modfied 75% of the land surface?



  • Agricultural intensity must match demand


  • Freshwater is a limiting resource
    • 40% dedicated to agriculture

    • deep water sources are needed
    • water needs to be diverted


  • Minerals and metals are needed for everything


  • Natural ecosystems provide materials
    • and get it the way

Human activities create contaminants


  • From point sources to diffuse impacts
    • California oil spill vs. fertilizer run-off in Chesapeake Bay

Human activities create contaminants: Excess carbon dioxide


Human activities create contaminants: Other greenhouse gases


Humans are now connected worldwide



  • The impacts of globalization on natural systems is huge


  • Humans move species around - for better or worse
    • necessary for food systems
    • unintentional has part of trade (invasive species)
    • intentional with unknown consequences


  • Infrastructure of globalization also disrupts natural systems
    • roads fragment landscapes
    • transportation pollutes
    • politics of trade divides wealth

How do stressors interact?


Synergy: when the total effect is more than the sum of the individual effects


Partially additive: when the total effect is less than the sum of the individual effects

Big picture: These stresses have altered Earth’s climate systems


The climate system is powered by solar radiation.


Incoming solar radiation balanced by outgoing radiation


If balance interupted, Earth warms or cools



The radiative balance can be perturbed by “forcings’


  • Each ‘forcing’ can alter:
    • incoming solar radiation (shortwave)
    • solar radiation that is reflected
    • longwave radiation emitted from Earth


  • Forcings largely a function of greenhouse gases
    • each absorb longwave radiation

Why does climate change over time?


Climate change is not new


Climate change then versus now…


5°C of “natural” warming took earth from an Ice Age to our modern interglacial world
Took 1600 years!

Climate change then versus now…


Contemporary climate change is different because of anthropogenic causes and velocity
Same 5°C change >10x faster

We measure current change since Industrial age…




  • Global mean surface temperature has risen ~ 1 degree C over the last 100 years


  • How much is left to come?
    • depends on continued forcing
    • we can predict (based on trends)
    • always some uncertainty

Future climate change is inevitable




  • Global mean surface temperature has risen ~ 1 degree C over the last 100 years


  • How much is left to come?
    • depends on continued forcing
    • we can predict (based on trends)
    • always some uncertainty

Temperature is just one part of Earth’s changing climate system


Next up: Friday Exam